Many prior attempts have been made to improve the properties of bismaleimide ("BMI") resins.
U.S. Pat. No. 4,218,598 and the abstract of Japanese Kokai 61/72025 (both assigned to Toshiba) teach the preparation of a BMI/aminophenol adduct, followed by a curing reaction in the presence of a diepoxide.
The abstract of Japanese Kokai 58/142912 (assigned to Toshiba) illustrates BMI compositions which contain a diepoxide and an aminosulfanilamide.
The abstract of Japanese Kokai 58/142913 (to Toshiba) teaches a composition which comprises BMI, a diepoxide and o-aminobenzamide.
U.S. Pat. No. 4,288,359 (to DuPont) describes the preparation of a BMI/diepoxide adduct, followed by a curing reaction in the presence of an aromatic amine.
Prior art relating to epoxy resin modification is also of general background relevance to the present invention. In particular, the use of "fortifiers" as additives to improve the properties of epoxy resins is disclosed in U.S. Pat. Nos. 4,739,028, 4,480,082 and 4,816,533, the disclosures of which are incorporated herein by reference. The term "fortifier" refers to an adduct of a selected epoxide and a second reactant which is chosen from specific amine, amide or polyhydroxyl compounds. In general, these fortifiers are low molecular weight materials with low melting points.
Fortifiers improve the strength properties of thermoset epoxy resins, without causing the thermoset to become brittle.
Heretofore, the reported use of the above fortifiers has been essentially restricted to epoxy resins. It has now been surprisingly discovered that selected "epoxy fortifiers" may be utilized to prepare thermoset bismaleimide resins having improved properties.